The present invention relates to new silicon containing monomers which are transparent at 193 nm and copolymers obtained from these silicon containing monomers. The copolymers of the present invention are especially suitable for forming radiation sensitive bilayer resists. The bilayer resists can be used in the manufacture of integrated circuits.
In the fabrication of integrated circuits, one of the more critical procedures is the lithographic processing. Improving lithographic techniques is a continuing demand in view of the ever increasing desire in the semiconductor industry for higher circuit density in microelectronic devices.
One method of achieving higher area density is to improve the resolution of circuit patterns in resist films. It is known in the art that increasing the numerical aperture (NA) of the lens system of the lithographic imaging tool increases the resolution at a given wavelength. However, increasing the NA results in a decrease in the depth of focus (DOF) of the imaging radiation, thereby requiring a reduction in the thickness of the imaging resist film. Further, the industry wide shift to shorter wavelength exposure systems also results in as decrease in the DOF. A decrease in the resist film thickness can lead to problems in subsequent processing steps (e.g., ion implantation and etching).
In order to overcome these problems, bilayer resists have been developed. Bilayer resists generally comprise a top thin film imaging layer coated on a thick organic underlayer. The resist is patterned by (i) imagewise exposure and development of the top layer, and then (ii) anisotropically transferring the developed pattern in the top layer through the thick underlayer to the substrate. Suitably, the top layer contains precursors to refractory oxides such as silicon, boron, or germanium which enable the use of oxygen-reactive ion etching (RIE) in the image transfer step.
Bilayer resists are known in the art, however, these resists were generally developed before the advent of deep U.V. lithography (e.g., 248 nm and 193 nm) and are of little utility for high resolution imaging. The silicon containing bilayer photoresists are one of the more attractive candidates for possible use for 248 nm applications. There is currently a need to develop materials for the next generation of exposure systems at 193 nm (and perhaps 157 nm) as well. Unfortunately current generation DUV bilayer resists are not extendible to shorter wavelengths due to poor transparency at these shorter wavelengths. This high absorbance is due in large part to the aromatic poly(hydroxystyrene) moiety found in nearly all DUV 248 nm resists. However, certain structural types of silicon monomers can also contribute to the high absorbance at 193 nm. For example, the 4SiMA monomer (see FIG. 1), a tetrasilane containing Sixe2x80x94Si linkages, is disclosed in U.S. Pat. No. 5,985,524, inter alia, for use in bilayer resists. This is a very useful bilayer resist component due to its high silicon density and correspondingly high O2-RIE etch resistance at relatively low monomer loadings. Low silicon monomer loadings are generally desirable since silicon often negatively impacts the resist dissolution characteristics. Low loadings also provide greater latitude in the design of the polymer.
Unfortunately, the presence of Sixe2x80x94Si bonding in this monomer leads to unacceptably high absorbance at 193 nm. For example, a methacrylate polymer containing only 20 mole percent of this monomer (see FIG. 2; other monomers in this polymer are nearly transparent) has an absorbance of 6 per micron film, which makes this monomer unsuitable for 193 nm applications.
It has also been suggested to use a commercially available Sixe2x80x94Oxe2x80x94Si containing monomer (see FIG. 3) in 193 nm bilayer resist development. See Schaedeli et al., xe2x80x9cBilayer Resist Approach for 193 nm Lithographyxe2x80x9d, Proc. SPIE, Vol. 2724, pp. 344-354, 1996. However, the introduction of silicon-oxygen functionality into the monomer can have deleterious consequences on the resist performance. Particularly, these siloxanes often have poor hydrolytic stability under the processing conditions employed in these chemically amplified resists. This in turn can result in crosslinking reactions which can negatively impact the dissolution properties. In some cases, crosslinking occurring during the polymer preparation have been observed.
More recently, Kessel et al, xe2x80x9cNovel Silicon-Containing Resists for EUV and 193 nm Lithographyxe2x80x9d, Proc. SPIE, Vol. 3678, pp. 214-220, 1999 describe a bilayer resist claiming to be suitable for 193 nm resist applications. However, the polymer in this resist (see FIG. 6) contains a silicon containing monomer with Sixe2x80x94Si linkages similar to monomers in U.S. Pat. No. 5,989,524. As stated above, this 4Si group absorbs strongly at 193 nm, making it unsuitable for 193 nm resist applications (see FIG. 4 in reference 3 for examples of the poorly defined images that are a consequence of high polymer absorption). It is therefore an object of the present invention to provide an improved 193 nm bilayer resist. Other objects and advantages will become apparent from the following disclosure.
The present invention relates to new polymerizable monomers having silicon containing groups separated from each other by a group X wherein the group X is non-reactive and is transparent at 193 nm, and containing polymerizable ethylenically unsaturated group.
The present invention also relates to polymers from (a) a polymerizable monomer having silicon containing groups separated from each other by a group X wherein the group X is non-reactive and is transparent at 193 nm, and containing polymerizable ethylenically group.
A still further aspect of the present invention is concerned with a process for generating a bilayer resist image on a substrate. The process comprises:
(a) coating a substrate with an organic underlayer;
(b) coating the organic underlayer with a top layer comprising:
(i) a radiation sensitive acid generator and
(ii) a polymer from a polymerizable monomer having silicon containing groups separated from each other by a group X wherein the group X is non-reactive and is transparent at 193 nm, and containing polymerizable ethylenically unsaturated group, and being acid labile;
(c) imagewise exposing the top layer to radiation;
(d) developing the image in the top layer; and
(e) transferring the image through the organic underlayer to the substrate.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.